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4. Pediatrics MCQs

Practice Set 306 of 334

This practice set contains high-yield board review questions covering key concepts in 4. Pediatrics. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 6101

Topic: 4. Pediatrics

A 4-year-old boy presents with short stature, frontal bossing, and rhizomelic shortening. Radiographs show narrowing of the interpedicular distances in the lumbar spine. What is the underlying pathophysiology of this condition?

. Defect in type 1 collagen synthesis
. Loss of function mutation in FGFR3
. Gain of function mutation in FGFR3
. Defect in sulfate transport
. Failure of osteoclast function

Correct Answer & Explanation

. Gain of function mutation in FGFR3

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene, which inhibits chondrocyte proliferation at the physis. This leads to rhizomelic dwarfism and spinal stenosis due to narrow interpedicular distances.

Question 6102

Topic: 4. Pediatrics

A newborn presents with micromelic shortening of limbs, severe clubfeet, "hitchhiker" thumbs, and cystic swelling of the pinnae. Radiographs show first metacarpals that are oval-shaped. Which of the following is the defective mechanism in this disorder?

. Cartilage oligomeric matrix protein (COMP) defect
. Gain of function in FGFR3
. Sulfate transport defect
. Type 1 collagen mutation
. Deficient endochondral ossification of secondary centers

Correct Answer & Explanation

. Sulfate transport defect

Explanation

Diastrophic dysplasia is caused by an autosomal recessive mutation in the SLC26A2 gene, resulting in a sulfate transport defect. This leads to undersulfated proteoglycans in cartilage matrix, presenting with cauliflower ears and hitchhiker thumbs.

Question 6103

Topic: 4. Pediatrics

A 5-year-old child presents with disproportionate short-trunk dwarfism, a barrel chest, and coxa vara. Ophthalmologic exam reveals high myopia. Radiographs show flattened vertebral bodies and delayed ossification of the femoral heads. What is the underlying genetic defect?

. Defect in type I collagen
. Defect in type II collagen
. Defect in type IV collagen
. Defect in FGFR3
. Defect in COMP

Correct Answer & Explanation

. Defect in type II collagen

Explanation

Spondyloepiphyseal dysplasia (SED) congenita is caused by a mutation in the COL2A1 gene, resulting in defective type II collagen. Clinical features include short-trunk dwarfism, coxa vara, and ocular issues like myopia and retinal detachment.

Question 6104

Topic: 4. Pediatrics

A 9-year-old child presents with a waddling gait, knee pain, and short stature. Radiographs reveal delayed, fragmented epiphyseal ossification centers and a "double-layered" patella on the lateral knee view. The most likely mutated gene encodes for which of the following proteins?

. Type II collagen
. Type X collagen
. Cartilage oligomeric matrix protein (COMP)
. Fibroblast growth factor receptor 3
. Core-binding factor subunit alpha-1 (CBFA1)

Correct Answer & Explanation

. Cartilage oligomeric matrix protein (COMP)

Explanation

Multiple Epiphyseal Dysplasia (MED) with a double-layered patella is classically associated with mutations in the Cartilage Oligomeric Matrix Protein (COMP) gene. It primarily affects the epiphyseal ossification centers, delaying their formation.

Question 6105

Topic: 4. Pediatrics

A 45-year-old male with achondroplasia presents with neurogenic claudication. Which of the following best describes the underlying pathophysiology of his skeletal dysplasia?

. Defective sulfation of cartilage glycosaminoglycans
. Gain-of-function mutation in FGFR3 inhibiting chondrocyte proliferation
. Loss-of-function mutation in FGFR3 accelerating ossification
. Defective type II collagen synthesis
. Mutation in the COMP gene

Correct Answer & Explanation

. Gain-of-function mutation in FGFR3 inhibiting chondrocyte proliferation

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene (G380R). This mutation excessively inhibits chondrocyte proliferation in the proliferative zone of the physis, leading to rhizomelic dwarfism and narrowed spinal pedicles.

Question 6106

Topic: 4. Pediatrics

A 10-year-old child presents with bilateral hip pain, a waddling gait, and normal height. Radiographs show small, irregular, and fragmented epiphyses with a "double-layer" appearance of the patella on the lateral knee radiograph. Which gene is most commonly mutated in this condition?

. FGFR3
. COL1A1
. COMP
. SLC26A2
. RUNX2

Correct Answer & Explanation

. COMP

Explanation

Multiple Epiphyseal Dysplasia (MED) is most commonly caused by mutations in the COMP (Cartilage Oligomeric Matrix Protein) gene. The "double-layer" patella is a pathognomonic radiographic finding for this condition.

Question 6107

Topic: 4. Pediatrics

A newborn is evaluated for severe short-limbed dwarfism. Examination reveals bilateral clubfeet, "hitchhiker" thumbs, and prominent swelling of the auricles. Which of the following is the underlying genetic defect?

. Mutation in the sulfate transporter gene SLC26A2
. Mutation in the cartilage oligomeric matrix protein
. Gain-of-function mutation in FGFR3
. Mutation in the COL2A1 gene
. Deletion of chromosome 22q11

Correct Answer & Explanation

. Mutation in the sulfate transporter gene SLC26A2

Explanation

Diastrophic dysplasia is an autosomal recessive condition caused by mutations in the SLC26A2 sulfate transporter gene. Classic findings include hitchhiker thumbs, cauliflower ears, and severe rigid clubfeet.

Question 6108

Topic: 4. Pediatrics

A 14-month-old child presents with a limp, mild fever, and a swollen knee. Aspiration yields purulent fluid. Gram stain is negative, but PCR confirms the presence of an organism. Given the patient's age and clinical presentation, which organism is increasingly recognized as a leading cause?

. Staphylococcus aureus
. Streptococcus pneumoniae
. Kingella kingae
. Haemophilus influenzae type b
. Pseudomonas aeruginosa

Correct Answer & Explanation

. Kingella kingae

Explanation

Kingella kingae is a fastidious Gram-negative organism that is now recognized as a leading cause of osteoarticular infections in children aged 6 months to 4 years. It is best detected via PCR or by inoculating synovial fluid directly into blood culture vials.

Question 6109

Topic: 4. Pediatrics

A 6-month-old male with achondroplasia presents with witnessed episodes of central apnea, poor head control, and hyperreflexia in the lower extremities. What is the most appropriate next step in management?

. Observation and reassurance as this is typical for achondroplasia
. Immediate halo gravity traction
. Polysomnography and continuous positive airway pressure (CPAP)
. MRI of the cervical spine to assess the foramen magnum
. Surgical suboccipital decompression and C1 laminectomy without prior imaging

Correct Answer & Explanation

. MRI of the cervical spine to assess the foramen magnum

Explanation

Central apnea and hyperreflexia in an infant with achondroplasia are major red flags for cervicomedullary compression. MRI is the diagnostic modality of choice to evaluate foramen magnum stenosis before proceeding to surgical decompression.

Question 6110

Topic: 4. Pediatrics

A 5-year-old boy sustains a low-energy femur fracture. On examination, he has blue sclerae and generalized osteopenia on radiographs. A genetic defect in which of the following is most likely responsible for his condition?

. Fibroblast growth factor receptor 3 (FGFR3)
. Cartilage oligomeric matrix protein (COMP)
. Type I collagen (COL1A1 or COL1A2)
. Sulfate transporter (SLC26A2)
. Type II collagen (COL2A1)

Correct Answer & Explanation

. Type I collagen (COL1A1 or COL1A2)

Explanation

Osteogenesis imperfecta is primarily caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes. This leads to quantitative or qualitative defects in type I collagen, the major structural protein in bone.

Question 6111

Topic: 4. Pediatrics

A 26-year-old female with a long-standing history of polyarticular Juvenile Idiopathic Arthritis is scheduled for a bilateral total hip arthroplasty. During preoperative templating and surgical planning, which anatomic deformity on the femoral side should the surgeon anticipate?

. Excessive femoral retroversion and an extremely wide canal
. Coxa vara and excessive femoral retroversion
. Excessive femoral anteversion and a narrow intramedullary canal
. Coxa magna and a champagne-flute medullary canal
. Severe trochanteric overgrowth with normal anteversion

Correct Answer & Explanation

. Excessive femoral anteversion and a narrow intramedullary canal

Explanation

Patients with severe JIA commonly develop hypoplastic bone anatomy due to early physeal closure and lack of normal weight-bearing. The proximal femur characteristically exhibits excessive anteversion, coxa valga, and an extremely narrow intramedullary canal.

Question 6112

Topic: 4. Pediatrics

A 4-year-old boy presents with rhizomelic short stature, frontal bossing, and midface hypoplasia. Radiographs reveal narrowing of the interpedicular distances in the lumbar spine. Which of the following genes is mutated in this condition?

. FGFR1
. FGFR2
. FGFR3
. COMP
. COL2A1

Correct Answer & Explanation

. FGFR3

Explanation

Achondroplasia is caused by an activating mutation in the FGFR3 gene, which inhibits chondrocyte proliferation in the proliferative zone of the physis. It presents with rhizomelic dwarfism and narrowing of the lumbar interpedicular distance, increasing the risk of spinal stenosis.

Question 6113

Topic: 4. Pediatrics

A newborn presents with short-limbed dwarfism, hitchhiker thumbs, bilateral severe clubfeet, and cystic swelling of the external ears. What is the genetic mechanism of this disorder?

. Activating mutation in the FGFR3 receptor
. Defect in a sulfate transporter for cartilage
. Mutation in the Type II collagen gene
. Mutation in the CBFA1 transcription factor
. Defect in cartilage oligomeric matrix protein

Correct Answer & Explanation

. Defect in a sulfate transporter for cartilage

Explanation

Diastrophic dysplasia is caused by a mutation in the SLC26A2 gene (DTDST), which leads to a defect in a sulfate transporter essential for cartilage proteoglycan sulfation. The presence of 'cauliflower ear' is pathognomonic.

Question 6114

Topic: 4. Pediatrics

A 10-year-old boy presents with bilateral knee and hip pain. Radiographs show delayed, irregular ossification of the capital femoral epiphyses and a double-layered patella on the lateral view. His spine is radiographically normal. Which of the following genes is most commonly mutated in this condition?

. COL2A1
. FGFR3
. COMP
. SLC26A2
. RUNX2

Correct Answer & Explanation

. COMP

Explanation

Multiple Epiphyseal Dysplasia (MED) is characterized by abnormal epiphyses with a normal spine, and a double-layered patella is a classic radiographic finding. It is most commonly caused by an autosomal dominant mutation in the COMP gene.

Question 6115

Topic: 4. Pediatrics

A 6-year-old child presents with a disproportionately short trunk, barrel chest, and coxa vara. Radiographs reveal delayed ossification of the pubic bones, platyspondyly, and a hypoplastic odontoid. What is the underlying genetic mutation associated with this condition?

. FGFR3
. COL1A1
. COL2A1
. COMP
. SLC26A2

Correct Answer & Explanation

. COL2A1

Explanation

This presentation is classic for spondyloepiphyseal dysplasia (SED) congenita, which is caused by a defect in type II collagen due to a COL2A1 gene mutation. Type II collagen is crucial for proper hyaline cartilage formation, affecting the spine and epiphyses.

Question 6116

Topic: 4. Pediatrics
A 14-month-old child presents with a limp, a temperature of 38.2°C, and refusal to bear weight on the right leg. Routine blood cultures are negative, but synovial fluid PCR detects the causative organism. Which of the following best describes the most likely organism responsible for this presentation?
. Gram-positive cocci in clusters
. Gram-negative diplobacilli
. Acid-fast bacilli
. Spirochete
. Fungal yeast

Correct Answer & Explanation

. Gram-negative diplobacilli

Explanation

Kingella kingae is a Gram-negative diplobacillus and is the most common cause of pediatric septic arthritis in children under 4 years old. It is fastidious and often requires specific BACTEC blood culture vials or PCR for detection.

Question 6117

Topic: 4. Pediatrics

A newborn presents with short-limbed dwarfism, bilateral rigid clubfeet, hitchhiker thumbs, and cystic swelling of the external ear. Which of the following genes is mutated in this condition?

. FGFR3
. COL1A1
. COMP
. SLC26A2
. RUNX2

Correct Answer & Explanation

. SLC26A2

Explanation

This describes diastrophic dysplasia, an autosomal recessive condition characterized by hitchhiker thumbs, cauliflower ears, and severe clubfeet. It is caused by a mutation in the SLC26A2 gene (also known as DTDST), which encodes a sulfate transporter.

Question 6118

Topic: 4. Pediatrics

A 5-year-old child presents with short-limbed dwarfism, a waddling gait, and joint laxity. The patient facial features and head circumference are completely normal. Radiographs show small, irregular epiphyses and metaphyseal flaring. What is the mutated gene?

. COMP
. FGFR3
. COL2A1
. COL1A1
. FBN1

Correct Answer & Explanation

. COMP

Explanation

Pseudoachondroplasia presents with short-limbed dwarfism but uniquely spares the craniofacial skeleton (normal face and head). It is caused by mutations in the Cartilage Oligomeric Matrix Protein (COMP) gene.

Question 6119

Topic: Pediatric Hip

A 12-year-old boy presents with bilateral hip and knee pain after physical activity. Radiographs reveal irregular, flattened epiphyses in the hips and knees, with a double-layer appearance of the patella on the lateral view. His height and spine radiographs are normal. What is the most likely diagnosis?

. Legg-Calve-Perthes disease
. Spondyloepiphyseal dysplasia
. Multiple epiphyseal dysplasia
. Chondrodysplasia punctata
. Pseudoachondroplasia

Correct Answer & Explanation

. Multiple epiphyseal dysplasia

Explanation

Multiple epiphyseal dysplasia (MED) affects the epiphyses of the appendicular skeleton, causing early-onset osteoarthritis and a classic double-layer patella on lateral radiographs. The spine is generally spared, differentiating it from spondyloepiphyseal dysplasia.

Question 6120

Topic: 4. Pediatrics

A newborn presents with short-limbed dwarfism, abducted "hitchhiker" thumbs, clubfeet, and cystic swelling of the pinnae that later develops into a "cauliflower ear" deformity. Radiographs demonstrate shortening of the tubular bones and a characteristic first metacarpal anomaly. Which of the following gene mutations is responsible for this condition?

. FGFR3 mutation
. COMP mutation
. SLC26A2 mutation
. RUNX2 mutation
. COL1A1 mutation

Correct Answer & Explanation

. SLC26A2 mutation

Explanation

This clinical presentation is classic for diastrophic dysplasia, an autosomal recessive condition. It is caused by a mutation in the SLC26A2 (DTDST) gene, which impairs the sulfate transporter essential for normal cartilage matrix formation.

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